1. Field of the Invention
This invention relates to a light emitting device comprising a light emitting diode (hereinafter referred to as “LED”) element as a light source and, in particular, to a light emitting device that has a high radiation performance for heat generated from the LED element and is excellent in productivity.
2. Description of the Related Art
LED is suitable for an application of a light source in view of an environmental protection and an electrical power saving. Therefore, LED is expected to be applied to a broad application such as a small sized electronics device, a lighting device and a lamp fitting as a white light source, as well as a substituting light source for a fluorescent lamp. According to this, recently, light emitting devices using LEDs of various types such as LED of a high output type and LED of a large light amount type have been proposed, but a problem of the heat accompanying the emission have become evident. Therefore, it becomes an important issue that how to ensure a high radiation performance in order to realize a light emitting device using LED of a high output type.
As an example of a LED light emitting device improved in a radiation performance, a light emitting device shown in a patent document of PCT International Publication Pamphlet No. 2005/043637 (7 page, FIG. 1, FIG. 9 FIG. 10 and FIG. 12) is known. The light emitting device comprises a radiation plate which comprises plate members composed of a high thermally-conductive material, mounts a light source part comprising a light emitting element as a light source, and is formed so as to comprise a radiation width disposed in a side of a back surface of the light source part.
The light emitting device shown in the patent document comprises a mounting part of the LED element in an edge surface of the radiation plate, and to slits formed at one of the radiation plates the other radiation plate is inserted so that two radiation plates are assembled to a cross-shaped plates and a radiation width is disposed in a side of a back surface of the LED element. Also, the radiation plate can be formed by an extrusion process.
According to the light emitting device shown in the patent document, a radiator is formed by assembling the radiation plates comprising a radiation width disposed in a direction parallel to a light axis of the LED element, so that a high heat conductivity can be realized without interfering with an emission property of a light emitted from the LED element and an atmosphere radiation performance can be enhanced.
However, in the light emitting device shown in the patent document there are the following problems.
(1) It is necessary to conduct a positioning for inserting and fixing of the radiation plates appropriately when the radiator is formed by assembling the radiation plates so that the assembling work becomes troublesome and then it becomes difficult to improve a productivity of the light emitting device.
(2) It is necessary to form the radiator so as to comprise a structural strength be capable of bearing with an extrusion process when the radiator is formed by the extrusion process so that it is limited to reduce a size of the light emitting device and a thickness of the radiation plates.